解析布爾表達式沒有左手遞歸

Question

我試圖匹配該

f(some_thing) == 'something else' 

• F（SOME_THING）是一個函數調用，它是一種表達
• ==是一個布爾運算符
• '別的東西'是一個字符串，它也是一個表達式

所以布爾表達式應該是

expression operator expression 

問題是我無法弄清楚如何做到這一點沒有左遞歸 這是我的規則

expression 
    = 
    bool_expression 
/function_call 
/string 
/real_number 
/integer 
/identifier 

bool_expression 
    = l:expression space* op:bool_operator space* r:expression 
    { return ... } 

使用語法符號，我有

O := ==|<=|>=|<|>|!= // operators 
E := B|....   // expression, many non terminals 
B := EOE 

因爲我的語法是EOE我不知道如何去用左手算法是

A := Ab|B 
transforms into 
A := BA' 
A':= e|bA 

其中E是空的，b是終端

Answer 1

像這樣的東西應該做到這一點：

expression 
= bool_expression 

bool_expression 
= add_expression "==" bool_expression 
/add_expression "!=" bool_expression 
/add_expression 

add_expression 
= mult_expression "+" add_expression 
/mult_expression "-" add_expression 
/mult_expression 

mult_expression 
= atom "*" mult_expression 
/atom "/" mult_expression 
/atom 

atom 
= function_call 
/string 
/real_number 
/integer 
/identifier 

function_call 
= identifier "(" (expression ("," expression)*)? ")" 

string 
= "'" [^']* "'" 

identifier 
= [a-zA-Z_]+ 

integer 
= [0-9]+ 

real_number 
= integer "." integer? 
/"." integer